Carburetters



July 22, 1969 G. L. LAWRENCE 3,456,929

. CARBURETTERS Filed Aug. 7, 1967 2 Sheets-Sheet l Figi.

July 22 1969 G. l.. LAWRENCE y 3,456,929

CARBURETTERS Filed Aug. 7, 1967 v 2 Sheets-Sheet 2 FLgZ i I0 22 36 I2 l]figg-l 1'1"' I United States Patent O 3,456,929 CARBURETTERS GeoffreyLloyd lLawr-enee, Stanmore, England, assigner to The Zenith CarhnretterCompany Limited, Honeypot Lane, Stanmore, lEngland Filed Aug. 7, 1967,Ser. No. 658,778 Ciaims priority, application Great Britain, Aug. 12,1966, 36,237/66; Apr. 20, 1967, 18,270/57 int. Ci. FtiZm 23/04 US. Cl.261--44 6 Claims ABSTRACT F THE DESCLQSURE To enable the air valves ofair valve carburetters to be set to provide a consistent lift of the airvalve for a given total weight of air ow, there is provided, in a'bypass passage past the air valve, an adjustable valve so that thetotal leakage, i.e. that due to manufacturing tolerances and thatthrough the adjustable valve, can be set to a standard. Separate controlof the total leakage flow to a limited extent may be provided for idlingadjustment.

This invention relates to carburetters of the air valve type in whichthe air valve is a slide valve movable transversely across the mixturepassage in the carburetter body so as to vary the cross-sectional areaof a gap between the inner end of the said slide valve and a fixedsurface in the said passage, which gap is hereinafter referred to as thethroat, the slide valve being movable to vary the said area bydifferential air pressure acting on the two sides of a diaphragm orpiston coupled to the slide valve.

The slide valve passes through an opening in the wall of the mixturepassage on the side of the latter opposite to the fixed surface, into ahousing which is divided into two chambers by the diaphragm or piston onwhich the differential air pressure acts, the rst chamber on the side ofthe diaphragm or piston nearest to the mixture passage being connectedto the ambient atmosphere or to a source of sub-atmospheric pressure.The second chamber, on the other side of the piston or diaphragm is incommunication With the mixing chamber of the carburetter, which is thepart of the mixture passage downstream of the air valve and upstream ofa throttle valve in the mixture passage, and a spring acts on the slidevalve to urge it towards the fixed surface in the mixture passage. Thethroat is considered as being situated downstream of the air valve,since the depression created by the air valve prevails in the throat.The pressure prevailing in the first chamber thus tends to lift theslide valve against the spring, the degree of lifting increasing as theair ow inspired `by the engine through the mixing chamber increases.

For a number of reasons, it is desirable to be able to alter theeffective flow capacity of the passage means into the mixing chamber tosome extent independently of the movement of the slide valve and thegeneral object of the present invention is to provide for suchalterations to be carried out.

Whilst the iiow of air past the slide valve will take place mainlythrough the gap between the said slide valve and the fixed surface someleakage flow will take place around the sides of the said valve andthrough clearance between the said slide valve and the opening in thebody through which it extends into the chamber on the side of thediaphragm nearest to the mixture passage, and in carburetters of thesame construction and size the leakage tiow will Vary from one toanother due to working tolerances in the manufacture of the parts andresulting differences in the clearance.

3,456,929 Patented July 22, 1969 ice Theoretically, the setting of thethrottle valves of a number of nominally identical carburetters to causean identical weight of air to iiow through all of them for idlingpurposes should result in equal flow rates of air through the gapbetween the slide valve and the fixed surface. In practice, due tovariations in the leak path, the air valve adjusts itself according tothe leakage and takes up a position which varies from one carburetter toanother. As a result, the quantity of fuel delivered into the airstream, as will be described hereinafter, depends on the actual positionof the slide valve, and the idling mixture will vary from onecarburetter to another.

It has been found that provision for small adjustments in the size ofthe passage means providing air flow other than through the gap betweenthe slide valve and the fixed surface may be advantageous in the settingof the carburetter for idling.

The movement of the slide valve controls the position of a needle in ajet orifice through which fuel is admitted to the gap between the saidslide valve and the fixed surface, so that the quantity of fuel drawninto the mixture passage, for a given depression acting on the jet,varies with the position of the said slide valve.

To avoid or reduce to a minimum the inclusion in the exhaust emission ofan internal combustion engine of toxic elements such as carbon monoxideand unburnt hydrocarbons it is essential that the fuel/air ratio of themixture supplied to the engine cylinders shall be closely controlled,and the present invention, by enabling a constant air valve position fora given weight of total air flow through the carburetter to be obtained,makes readily possible the achievement of a correct ratio.

According to the present invention, in an air valve carburetter forinternal combustion engines comprising an induction passage, a housingadjacent to said induction passage and divided into a first chamber anda second chamber by a movable wall, a slide valve connected to saidmovable wall and slidably movable with clearance through an opening inthe wall of the induction passage, said opening connecting saidinduction passage and said first chamber, the said slide valveco-operating with a part of the wall of the induction passage to providea variable gap, biasing means acting on said slide valve to urge ittowards said -wall part, a mixing chamber formed in the inductionpassage between the slide valve and a throttle valve downstream of saidslide valve, the said second chamber being connected to the mixingchamber whereas the said first chamber is arranged to receive air at apressure greater than that existing in the mixing chamber, air ow intothe mixing chamber additional to ow through the said gap is adjustableby means of at least one valve in passage means through which a part ofsaid additional ow passes.

Two valves may be provided, each of which is adapted to alter the owcapacity of said passage means, and the said passage two means maycomprise two separate passages controlled respectively by one and theother of the said two valves. One of the two valves may provide for arelatively large range of adjustment whereas the other of said valvesprovides for a relatively small range of adjustment.

Means may be provided for sealing one of the said valves so that itcannot be adjusted except by removal of the seal, and the said sealingmeans may be provided for the valve providing the larger range ofadjustment.

The said passage means may provide a connection between the mixingchamber of the carburetter and the said first chamber, the valve in saidpassage being adjustable to a fixed setting.

The invention is hereinafter described with reference to theaccompanying drawings, in which:

FIGURE 1 is a sectional elevation of one form of air valve carburetterembodying the invention; and

FIGURE 2 is a section of the carburetter taken on the line 2--2 ofFIGURE 1.

In the illustrated embodiment of the invention there is shown two valvesboth of which are independently operable to vary the flow of air intothe mixing chamber of the carburetter, but it will be understood thatone of these valves may be omitted if adjustment of the air flow for oneof the purposes hereinbefore set forth is not required.

Referring to the drawings, the carburetter comprises a body throughwhich extends a mixture passage 11 of circular cross section. An airvalve in the form of a slide valve 12, slidable transversely of thepassage 11, extends through an opening 13 at one side of the mixturepassage, the said slide valve 12 having a flat surface 14 whichco-operates with a flat fixed surface 15 in the mixture passage, lyingon a chord to the circumference of the said passage, to provide a throat16 the area of which varies with the position of the slide valve 12. Thesurface 15 is formed on a bridge 17 having sloping side surfaces at 18and 19 so that the area of the throat decreases and increasesprogressively on opposite sides of the surface 15.

A buttery throttle valve 21 is provided in the mixture passage 11downstream of the slide valve 12, the space 22 between the said throttlevalve 21 and slide valve 12 forming a mixing chamber.

The slide valve 12 extends into a housing, formed partly in thecarburetter body 10 and partly by a separate cap member 23. A flexibleannular diaphragm 24, clamped at its inner edge to the slide valve 12and at its outer edge between the carburetter body 10 and the cap member23, divides the housing into two chambers 25 and 26, the chamber 25, onthe side of the diaphragm 24 remote from the mixture passage 11, beingconnected to the mixing chamber 22 by an opening 27 in the slide valve12. The chamber 26 is connected at 28 to the atmosphere. The carburetteris normally mounted with the housing uppermost, so that the weight ofthe slide valve 12 tends to urge it towards the surface 15, and a lightspring 29 is provided to further bias it in the same direction. Adashpot device 31 is provided to damp the movements of the slide valve12. The diaphragm 24 may be replaced by a piston sliding in a cylinder.

A fuel supply chamber 32 is provided below the bridge 17, in whichliquid fuel supplied by a pump from a fuel tank in the conventionalmanner is maintained at a desired level by an inlet valve (not shown)controlled by a pivoted oat 33. A fuel jet 34 mounted in the bridge 17enables fuel from the chamber 32 to be drawn'into the mixture passage 11by air flow across the said jet 34, a tapered needle 35 carried by theslide valve 12 being provided to vary the effective area of the jet inaccordance with the position of the said slide valve.

Th carburetter as so far described is substantially of conventionalform, and it will be understood that, when air is being drawn throughthe mixture passage by the suction in the cylinders of an internalcombustion engine to which the carburetter is connected, depressioncreated in the mixing chamber will also act in the chamber 2S, so thatatmospheric air pressure acting in the chamber 26 will tend to lift theslide valve 12 and increase the area of the throat 16, thus varying theair flow to keep the depression substantially constant. Since thedepression will tend to increase as the throttle valve opens, the slidevalve 12 will lift as the throttle valve opens, to increase the ow ofair into the mixing chamber, and at the same time increase the flow offuel from the jet 34.

It has already been stated that some leakage flow of air into the mixingchamber 22 will take place through clearance around the sides of theslide valve 12 (at 36 in FIGURE 2), and through the opening 13, and thatsuch leakage flow will aect the flow rate of air through the throat 16when a given weight of air flows through the carburetter. Since thequantity of fuel delivered into 4. the air stream depends on the lift ofthe slide valve, the idling mixture will vary from one to another ofnominally identical carburetters.

To enable a standard flow rate to be achieved, it is necessary toprovide for the adjustment of the total flow of air additional to thatwhich passes through the throat, and to enable such adjustment to beprovided, a passage is formed in the carburetter body 10 connecting themixing chamber 22 to the chamber 26, and a valve is provided to controlthe air flow through this passage. Referring to FIGURE 1, a bore 37 isformed, extending from the exterior of the carburetter body into themixing chamber 22, the outer part of the bore 37 being screw-threaded at38, and a step being formed at 39 adjacent the inner end of the bore. Acounterbore 41 is provided at the outer end of the screwthreaded part38. A second bore 42 extends from the chamber 26 so as to intersect thebore 37 between the screwthreaded part 38 and the step 39. Ascrew-threaded plug 43 engaging the screw-threaded part 38 of the bore37 has integral with it a tapered needle 44 extending past the step 39so that, by screwing the plug 43 in or out, the effective area of thepassage formed by the hores 37 and 42 can be varied. The plug 43 has ascrew-driver slot 45 to enable it to be manipulated, and is of such alength that it lies wholly within the body 10, enabling the bore 37 tobe sealed by a sealing disc 46 pressed into the counterbore 41.

Since the chamber 26 is in communication with the atmosphere, thepassage constituted by the bores 37 and 42 is, in effect, in parallelwith the leakage paths, and adjustment of the valve needle 44 will varythe total leakage flow and enable all of a number of nominally identicalcarburetters to be set to provide a standard air flow rate through thethroats thereof.

It will be understood that the valve controlled passage, instead ofleading from the chamber 26 into the mixing chamber 22 may lead from anyother point at which air at or near atmospheric pressure is available,and the valve may be of any suitable type. A needle valve is preferredsince it is capable of fine adjustment.

In order to compensate for a relatively wide range of differences of airleakage in the carburetters, the needle valve 44 is provided with arelatively long tapered needle.

It is desirable that, once the needle valve 44 has been set, it shallnot be disturbed, and consequently, if adjustment of air flow past theslide valve 12 is required for purposes other than to set thecarburetter to a standard by compensating for differences of leakage dueto varying clearances, separate provision for such other purposes shouldbe provided.

Referring to FIGURE 2 of the drawings, a passage 47 is provided in thecarburetter body 1t) alongside the mixture passage 11, leading from theend of the body at which the air enters. The other end of the passage 47is closed, and it is intersected adjacent the closed end by a transversepassage 48 leading from the exterior of the body 10 into the mixingchamber 22. The transverse passage 48 is screwthreaded at its outer end,at 49, and is stepped at 51 between its inner end and its intersectionwith the passage 47. A needle valve to control the How of air in thepassages 47, 48 is provided by a screw plug 52 carrying a tapered needle53 at its inner end to co-operate with the step 51. The screw plug 52 isscrewed into the transverse passage 48 and is provided with a locknut52a to enable it to be locked in any position to which it is set. Thetapered needle 53 has a relatively short tapered portion and arelatively small included angle, so that the range of adjustmentprovided is considerably less than that provided by the needle valve 44,and is extended, at its smaller end, by a cylindrical portion 54 of alength such that it extends past the step 51 so long as the screw threadon the plug 52 engages with the screw thread in the passage 48, thusensuring that the effective area of the passage cannot exceed apredetermined maximum. Thus, by adjusting the plug 52 a small change inthe air flow through the passage 48 and consequently in the total air owpast the air valve piston or slide 12 can be made without altering theposition of the plug 43, to provide fine adjustment of the fuel/airmixture at idling speeds of the engine. Such variation is required tocompensate for engine stiffness and other characteristics. The range ofadjustment is limited to ensure that adjustment of the plug 52 cannotalter the fuel/air ratio suiciently to increase the content of toxicelements such as carbon dioxide and hydrocarbons in the exhaustemission.

I claim:

1. In an air valve carburetter for internal combustion enginescomprising an induction passage, a housing adjacent to said inductionpassage and divided into a first chamber and a second chamber by amovable wall, a slide valve connected to said movable wall and slidablymovable with clearance through an opening in the wall of the inductionpassage, said opening connecting said induction passage and said firstchamber, said slide valve co-operating with a part of the wall of theinduction passage to provide a variable gap, biasing means acting onsaid slide valve to urge it towards said wall part, a mixing chamberformed in the induction passage between the slide valve and a throttlevalve downstream of said slide valve, said second chamber beingconnected to the mixing chamber whereas said first chamber is arrangedto receive air at a pressure greater than that existing in the mixingchamber, the improvement comprising passage means for the ow of air intothe mixing chamber additional to the flow through said gap, a firstvalve in said passage means adjustable to vary the air ow in saidpassage means over a relatively large range and a second valve in saidpassage means adjustable to vary the air flow in said passage means overa considerably smaller range, wherein air flow into the mixing chamberadditional to fiow through said gap is adjustable by means of at leastone valve in passage means through which a part of said additional flowpasses.

2. An air valve carburetter according to claim 1 wherein the passagemeans comprises two separate passages, the first valve being provided inone of said passages and the second valve being provided in the other ofsaid passages.

3. An air valve carburetter according to claim 1, wherein sealing meansare provided for said first valve, having the larger range ofadjustment, so that it cannot be adjusted except by removal of the seal.

4. An air valve carburetter according to claim 1 wherein said first andsecond valves are needle valves.

5. An air valve carburetter according to claim 1 wherein said passagemeans provide a connection between the mixing chamber of the carburetterand the first chamber, said first valve, having the larger range ofadjustment, being in said passage and adjustable to a fixed setting.

6. An air valve carburetter according to claim 5 wherein said firstvalve is a needle valve carried by a screw plug mounted in a boreextending to the exterior of the carbureter.

References Cited UNITED STATES PATENTS 3,078,079 2/ 1963 Mick.

3,147,320 9/ 1964 Tubb 261-44 X 3,198,498 8/ 1965 Mennesson.

3,243,167 3/1966 Winkler 261-44 3,321,195 5/1967 Korte.

3,342,463 9/ 1967 Date et al 261--44 3,351,327 11/1967 Simonet et al.

. FOREIGN PATENTS 1,429,365 1/ 1966 France.

TIM R. MILES, Primary Examiner U.S. Cl. X.R.

